The consortium of GE Global Research, U. of Michigan, and Stanford University proposes the development of a novel breast imaging device based on the use of silicon micro-machined ultrasound transducer (MUT) arrays placed on both upper and lower compression plates in a manner similar to mammography. The goal is to create a highly flexible and ideal breast ultrasound imager. By the use of semi-conductor devices, the entire surface of both compression plates can be made to function as reconfigurable transducer arrays. Reconfigurabilty refers to the ability to group small array elements ("pixels") to form larger arrays in any desired configuration such as an annular array or any other desirable configuration. This arrangement has numerous clinical advantages such as forming compound images of a lesion using data from both the upper and lower plates (minimize shadowing artifacts) and the ability to adjust the aperture and its elements into sizes appropriate for the patient being examined. Complete 3D data sets can be acquired in renderings made with 3D compounding to optimize achievable contrast and maximize speckle suppression. The annular array aperature will result in the thinnest possible slice thickness which, unlike existing devices, will be dynamically focused over the entire depth. Novel breast imaging methods can be devised such as 2D speed of sound or attenuation measurements by through-transmission. Imaging techniques such as elastography can be applied in a more rigorous manner than before including use of 3D. The specific aims identify key development steps needed to be accomplished in order for the device to be fabricated and its performance validated initially in a test tank and finally in a clinic with a preclinical assessment. Main fabrication challenges involve the very large scale integration of MUT devices with a switch-matrix and pulser/pre-amp electronics. These will be composed of smaller (0.5-1.0 cmA2) chips which will be tiled to cover the entire surface.